It has been recognized for some years that it is very desirable to be able to change the elevation of the lower unit of an outboard motor mounted on a boat, not only to permit the propeller to avoid striking submerged obstructions and to permit the boat to be propelled through shallow water, but also to adjust the operating elevation of the propeller relative to the bottom of the boat to achieve optimum drive efficiency for a particular boat, speed and loading thereof. As outboard motors have become heavier, power assist devices have been included in the mounting, as taught for instance by U.S. Pat. No. 3,096,959 to Wagner and U.S. Pat. No. 3,107,074 to Fowler.
U.S. Pat. No. 3,809,343 to Adams shows an hydraulic cylinder and telescoping guide means which is not intended to make elevation adjustments to improve operating trim at cruising speeds, but instead serves the purpose of simultaneously elevating the entire motor with respect to the transom and also tilting it into a storage position in which the lower unit of the motor is well clear of the water.
U.S. Pat. No. 3,421,723 to Holt provides an hydraulic adjustable-height mounting which straddles the transom of the boat for the purpose of avoiding the necessity of drilling any mounting holes through the transom. U.S. Pat. No. 2,775,219 to Curtis also shows a mounting which straddles the transom. Both of these patents show slide means aft of the transom and hydraulic cylinders inside the boat forward of the transom for elevating the slide means which carries the motor.